Given the shortage of conventional energy sources (e.g., oil), many efforts have been spent on exploring alternative energy sources. Among them, plant biomass is of particular interest as it is renewable.
Plant mass contains a high amount of cellulose, a starting material for making biofuel. To convert cellulose to biofuel, it is first degraded to fermentable sugars, such as cellobiose and glucose, by the cellulolytic system of microorganisms. This system includes three major types of hydrolases, i.e., endoglucanases (EC 3.2.1.4), exoglucanases (EC 3.2.1.91), and β-glucosidases (EC 3.2.1.21). Many cellulolytic enzymes have been isolated from various microorganisms, most of which exhibit optimal enzymatic activities at temperature below 50° C. As such, these enzymes do not efficiently degrade cellulose, the crystalline structure of which is typically destroyed above 50° C. Thus, there is a need for an efficient and thermophilic cellulolytic enzyme.